Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer in both children and adults, accounting for 90% of all liver cancers. It is the third leading cause of cancer-related mortality worldwide and the incidence of HCC has been rising in the United States and Europe over the past decades. In the U.S., liver cancer is among the top 10 most common cancers with the highest incidence rates among Asian Americans. Chronic infection with hepatitis B virus (HBV) or hepatitis C virus (HCV) is by far the most important risk factor for liver cancer. Clinical practice guidelines for the diagnosis, staging and treatment of HCC did not exist in the U.S. until the 2005 publication of the practice guideline for the management of hepatocellular carcinoma developed by the American Association for the Study of Liver Diseases (AASLD). The guideline recommended the use of ultrasound, CT scan, and MRI for the diagnosis of HCC with typical features. Biopsy is considered unnecessary if the imaging tests show typical features of HCC. Biopsy is recommended only when the vascular profile on imaging is not characteristic of HCC. In its 2009 position paper, the AASLD reaffirmed its stance on the role of liver biopsy in diagnosing and treating HCC. Under these practice guidelines, many liver cancer patients in recent years either do not have pathology reports or are not hospitalized for treatment, which jeopardizes completeness of liver cancer reporting in the population-based cancer registry system that heavily relies on these means for routine case-finding. Surveillance for HCC is of particular importance in California which has a large Asian/Pacific Islander population at high risk for this cancer. A recent published analysis of cancer trends in California showed while incidence rates were highest among Asian/Pacific Islanders, there was an increase of liver cancer in all race/ethnicity and gender groups between 1988 and 2005. If HCC is under ascertained, and if that under ascertainment is increasing because of recent changes in diagnostic practice, then we may be underestimating the magnitude of the problem. California also is the home of the Asian American Network for Cancer Awareness, Research and Training (AANCART). A current AANCART project is to increase screening for Hepatitis B in high risk populations. Evaluation of this intervention is at risk if HCC is incompletely ascertained. Given that these clinical guidelines for liver cancer are rather recent and that they are recommendations rather than requirements, their impact on the completeness of liver cancer reporting may have not yet been obvious in cancer registry reports. An earlier evaluation of HCC reported that 51 out of 909 (6%) of HCC cases diagnosed between 2000 and 2007 were missed by both the hospital which had a unified record and the SEER registries. Most of the HCC cases missed by the hospital registry were diagnostically confirmed by radiology. Scientists recently conducted a limited linkage of 60 HCC patients seen in 2009 at the Liver Transplant Program with the registry database. They found no records in this database for 24 (40%) of these cases. The higher proportion of missing cases is likely because the hospital registrars in the previous study has access to the unified medical records for their patients, registrars in this study depend primarily on pathology reports for casefinding. PHI will further investigate these and other potential missing HCC cases and identify systematic inadequacies in the current registry case-finding and case-reporting mechanisms for liver cancer, in relation to the emerging clinical practice patterns of liver cancer.